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Claims  |
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We claim:
1. A method used in a fixed system receiver for improving response
reception in a radio communication system having a forward radio channel
and a reverse radio channel, wherein a command is transmitted in a forward
channel radio signal by a fixed transmitter to a selective call
transceiver, and wherein the method comprises the steps of:
receiving, demodulating, and decoding the command within a forward
receiver, which command also includes an address of the selective call
transceiver and a scheduled response time at which the selective call
transceiver transmits a reverse channel radio signal comprising a data
unit, and which command includes a designated length of the data unit;
determining a response period beginning substantially at the scheduled
response time and having a duration which is substantially the designated
length of the data unit; and
receiving and demodulating the reverse channel radio signal within a
reverse receiver during the response period.
2. The method according to claim 1, further comprising the step of
disabling reception within the reverse receiver during periods which are
not the response period.
3. The method according to claim 1, wherein a plurality of commands are
transmitted in the forward channel radio signal by the fixed transmitter
to one or more selective call transceivers, wherein said step of
receiving, demodulating, and decoding is repeated for each of the
plurality of commands, the method further comprising the steps of:
determining one or more response periods, each corresponding to one of the
plurality of commands, each response period beginning substantially at the
scheduled response time included in the one of the plurality of commands,
and having a duration which is substantially the designated length of the
data unit included in the one of the plurality of commands; and
receiving and demodulating reverse channel radio signals within the reverse
receiver during the one or more response periods.
4. The method according to claim 3, further comprising the step of
disabling reception within the reverse receiver during periods which are
not the one or more response periods.
5. The method according to claim 1, further comprising the steps of:
decoding a received data unit at the scheduled response time; and
routing the received data unit to a system controller when the received
data unit has the designated length of the data unit, and otherwise
terminating processing of the received data unit.
6. The method according to claim 1, further comprising the steps of:
decoding a received data unit at the scheduled response time; and
routing the received data unit to a system controller when the received
data unit has the address of the selective call transceiver, and otherwise
terminating processing of the received data unit.
7. A fixed system receiver for use in a radio communication system having a
forward radio channel and a reverse radio channel, wherein a command is
transmitted in a forward channel radio signal from a system controller by
a fixed transmitter to a selective call transceiver, and wherein the fixed
system receiver comprises:
a forward receiver for receiving, demodulating, and decoding the command,
which command includes an address of the selective call transceiver and a
scheduled response time at which the selective call transceiver transmits
a reverse channel radio signal comprising a data unit, and which command
includes a designated length of the data unit;
a reverse receiver for receiving and demodulating the reverse channel radio
signal; and
a response timer, coupled to said forward receiver and said reverse
receiver, said response timer for determining a response period beginning
substantially at the scheduled response time and having a duration which
is substantially the designated length of the data unit, and for
generating a control signal which enables said reverse receiver during the
response period.
8. The fixed system receiver according to claim 7, wherein said response
timer disables said reverse receiver at times which are not the response
period.
9. The fixed system receiver according to claim 7,
wherein a plurality of commands are transmitted in the forward channel
radio signal by the fixed transmitter to one or more selective call
transceivers, and
wherein each command includes an address of one of the one or more
selective call transceivers, a scheduled response time at which the one of
the one or more selective call transceivers transmits a reverse channel
radio signal comprising a data unit, and a designated length of the data
unit, and
wherein said forward receiver receives, demodulates, and decodes one or
more of the plurality of commands, and
wherein said response timer determines one or more response periods
corresponding to one of the one or more of the plurality of commands, each
response period beginning substantially at the scheduled response time and
having a duration which is substantially the designated length of the data
unit, and
wherein said response timer generates a control signal which enables said
reverse receiver during the one or more response periods, and disables
said reverse receiver during times which are not the one or more response
periods.
10. The fixed system receiver according to claim 7 wherein the forward
channel radio signal and reverse channel radio signal are at a first radio
carrier frequency.
11. The fixed system receiver according to claim 10 wherein said forward
receiver and said reverse receiver are a combined receiver.
12. The fixed system receiver according to claim 7 wherein the forward
channel radio signal is at a first radio carrier frequency and the reverse
channel radio signal is at a second radio carrier frequency.
13. The fixed system receiver according to claim 12 wherein the command is
transmitted by the radio communication system at the second radio carrier
frequency.
14. The fixed system receiver according to claim 13, wherein said forward
receiver and said reverse receiver are a combined receiver.
15. The fixed system receiver according to claim 7,
wherein the forward receiver is a telephone interface, and
wherein the command is transmitted from the system controller over a
telephone network in an digital signal to the fixed system receiver.
16. The fixed system receiver according to claim 7, further comprising a
controller, coupled to said forward receiver and said reverse receiver,
said controller for decoding a received data unit from the demodulated
reverse channel radio signal received at the scheduled response time.
17. The fixed system receiver according to claim 16, wherein said
controller routes the received data unit to the system controller when the
received data unit has the designated length of the data unit, and
otherwise terminates processing of the received data unit.
18. The fixed system receiver according to claim 16, wherein said
controller routes the received data unit to the system controller when the
received data unit includes a transceiver address which matches the
address of the selective call transceiver, and otherwise terminates
processing of the received data unit.
19. The fixed system receiver according to claim 7 wherein the forward
radio channel has a plurality of forward channel frame boundaries and
wherein the scheduled response time is relative to one of the plurality of
forward channel frame boundaries.
20. The fixed system receiver according to claim 19 wherein a reverse
channel frame boundary, which is relative to one of the plurality of
forward channel frame boundaries, is included in the command, and wherein
the scheduled response time is relative to the reverse channel frame
boundary.
21. A fixed system receiver for use in a radio communication system having
a forward radio channel and a reverse radio channel, wherein a command is
transmitted in a forward channel radio signal by a fixed transmitter to a
selective call transceiver, and wherein the fixed system receiver
comprises:
a combined receiver for receiving, demodulating, and decoding the command
included in the forward channel radio signal having a first radio carrier
frequency, which command includes an address of the selective call
transceiver and a scheduled response time at which the selective call
transceiver transmits a reverse channel radio signal having the first
radio carrier frequency, said reverse channel radio signal comprising a
data unit, and which command includes a designated length of the data
unit, said combined receiver also for receiving and demodulating the
reverse channel radio signal;
a response timer, coupled to said combined receiver, said response timer
for determining a response period beginning substantially at the scheduled
response time and having a duration which is substantially the designated
length of the data unit, and for generating a control signal which enables
said combined receiver during the response period and disables said
combined receiver at times which are not the response period; and
a controller, coupled to said combined receiver, said controller for
decoding a received data unit from the demodulated reverse channel radio
signal received at the scheduled response time, for routing the received
data unit to a system controller when the received data unit has the
designated length of the data unit and when the received data unit
includes a transceiver address which matches the address of the selective
call transceiver, and otherwise terminating processing of the received
data unit, and
wherein the forward radio channel has a plurality of forward channel frame
boundaries and wherein a reverse channel frame boundary, which is relative
to one of the plurality of forward channel frame boundaries, is included
in the command, and wherein the scheduled response time is relative to the
reverse channel frame boundary. |
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Claims |
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Description |
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Field of the Invention
This invention relates in general to a selective call radio communication
system providing a received message response and in particular to a
message response in a selective call radio communication system having
fixed system receivers and scheduled response messages.
BACKGROUND OF THE INVENTION
In a selective call radio communication system having a forward channel for
transmitting digital messages to selective call transceivers from a system
controller and receiving digital messages and responses at the system
controller from the selective call transceivers in one or more reverse
channels, a known means of organizing the responses in the reverse
channels is to schedule the responses, using information transmitted in
the forward channel to the selective call transceivers to perform the
scheduling. This is a general approach used in a variety of radio systems.
A first example of such a system is a single frequency half duplex system
having one or more transmitters for transmitting the digital messages at a
radio carrier frequency from the system controller and one or more fixed
receivers for receiving the messages and responses from the selective call
transceivers on the same radio carrier frequency. The transmissions from
the system controller are typically suspended to allow responses from the
selective call transceivers. The responses may be transmitted from the
selective call transceivers using a random or semi-random method, or they
may be organized by information transmitted from the system controller.
The organized method works particularly well in a system having a large
percentage of acknowledgments or other demand type of responses. The
demand type of responses can be scheduled during the transmission from the
system controller which generates the demand responses. The selective call
transceivers can include in random responses information indicating to the
system controller that additional messages are being held within the
selective call transceivers, awaiting scheduled transmission to the system
controller. With this information, the system controller can schedule the
held messages for transmission on the reverse channel.
A second example of a system using scheduled responses in a reverse channel
is a duplex system having one or more transmitters for transmitting the
digital messages at a radio carrier frequency from the system controller
and one or more fixed receivers for receiving the messages and responses
at a second radio carrier frequency from the selective call transceivers.
In this system, the transmissions from the system controller do not need
to be stopped to allow responses from the selective call transceivers.
However, the responses may be organized, as in the case of the first
example, by information transmitted from the system controller.
In the case of both examples, some generic parameters of the scheduled
reverse channel transmissions are used by the fixed receivers for
recovering the reverse channel information from the transmissions made by
the selective call transceivers. For example, predetermination of the
modulation and bit rate to be received in the reverse channel is typically
needed by the fixed receivers to properly recover the reverse channel
information. Also, in a half duplex system, the fixed receiver may need a
predetermination of when the radio frequency is being used for the reverse
channel, to avoid misinterpreting information that is actually forward
channel information as reverse channel information. The message and
response information communicated within systems such as given in the
examples described above may be transmitted in packets of one or more
predetermined fixed lengths. A first packet of a group of packets, or a
single packet, transmitted by a selective call transceiver typically
includes a packet synchronization portion at the start of the packet,
which provides bit synchronization and identifies the beginning of a
second portion of the packet consisting of data words. Packets in a group
of packets, which are not the first packet of the group, may derive their
bit and word synchronization from the first packet in the group and
therefore not include a synchronization portion.
Using the predetermined modulation and reverse channel timing information,
a fixed receiver can recover most of such packets transmitted in the
reverse channel by the selective call transceivers, when the packets are
received within radio signals having a signal strength above a minimum
threshold. However, there are circumstances which may prevent the fixed
receivers from recovering some of these radio packets. These circumstances
arise when the fixed receiver's synchronization pattern detector is falsed
by noise, resulting in a false detection of a synchronization pattern,
further resulting in a false indication of the beginning of the word
portion of a packet. When this happens, the fixed receiver can miss the
decoding of the synchronization pattern and code words for a transmitted
packet because the fixed receiver is incorrectly processing data symbols
from the transmitted packet which are out of word synchronization
sequence, due to the false detection of a synchronization pattern prior to
the actual start of the transmitted packet. As a result of such false
synchronization detections, packets and groups of packets are not decoded
that otherwise could be, and the message throughput and message
sensitivity performance characteristics are therefore not as good as they
otherwise could be.
Thus, what is needed is a method to improve the message sensitivity and
message throughput performance characteristics in digital radio
communication systems having a forward and reverse channel and using
forward channel scheduling for messages and responses transmitted in the
reverse channel by one or more selective call transceivers
SUMMARY OF THE INVENTION
Accordingly, in a first aspect of the present invention, a method is used
in a fixed system receiver for improving response reception in a radio
communication system having a forward radio channel and a reverse radio
channel. A command is transmitted in a forward channel radio signal by a
fixed transmitter to a selective call transceiver. The fixed system
receiver includes a forward receiver and a reverse receiver. The method
includes the steps of receiving, demodulating, and decoding the command,
determining a response period, and receiving and demodulating the reverse
channel radio signal.
In the step of receiving, demodulating, and decoding the command, which is
performed in the forward receiver, the command, which includes an address
of a selective call transceiver and a scheduled response time at which the
selective call transceiver transmits a reverse channel radio signal
including a data unit is received, demodulated, and decoded. The command
includes a designated length of the data unit. In the step of determining
a response period, a response period is determined which begins
substantially at the scheduled response time and has a duration which is
substantially the designated length of the data unit. In the step of
receiving and demodulating the reverse channel radio signal, the reverse
channel radio signal transmitted by the selective call transceiver during
the response period is received and demodulated.
Accordingly, in a second aspect of the present invention, a fixed system
receiver is for use in a radio communication system having a forward radio
channel and a reverse radio channel. A command is transmitted in a forward
channel radio signal by a fixed transmitter to a selective call
transceiver. The fixed system receiver includes a forward receiver, a
reverse receiver, and a response timer.
The forward receiver is for receiving, demodulating, and decoding the
command included in the forward channel radio signal. The command includes
an address of a selective call transceiver and a scheduled response time
at which the selective call transceiver transmits a reverse channel radio
signal including a data unit. The command includes a designated length of
the data unit.
The reverse receiver is for receiving and demodulating the reverse channel
radio signal.
The response timer, which is coupled to the forward receiver and the
reverse receiver, is for determining a response period beginning
substantially at the scheduled response time and having a duration which
is substantially the designated length of the data unit, and for
generating a control signal which enables the reverse receiver during the
response period.
Accordingly, in a third aspect of the present invention, a fixed system
receiver is for use in a radio communication system having a forward radio
channel and a reverse radio channel. A command is transmitted in a forward
channel radio signal by a fixed transmitter to a selective call
transceiver. The fixed system receiver includes a combined receiver, a
response timer, and a system controller.
The combined receiver is for receiving, demodulating, and decoding the
command. The command is included in the forward channel radio signal
having a first radio carrier frequency. The command includes an address of
a selective call transceiver and a scheduled response time at which the
selective call transceiver transmits a reverse channel radio signal having
the first radio carrier frequency. The reverse channel radio signal
includes a data unit. The command includes a designated length of the data
unit. The combined receiver is also for receiving and demodulating the
reverse channel radio signal.
The response timer, which is coupled to the combined receiver, is for
determining a response period beginning substantially at the scheduled
response time and having a duration which is substantially the designated
length of the data unit. The response timer is also for generating a
control signal which enables the combined receiver during the response
period and disables the combined receiver at times which are not the
response period.
The system controller, which is coupled to the combined receiver, is for
decoding a received data unit from the demodulated reverse channel radio
signal received at the scheduled response time. The system controller is
also for routing the received data unit to a system controller when the
received data unit has the designated length of the data unit and when the
received data unit includes a transceiver address which matches the
address of the selective call transceiver, and is for terminating
processing of the received data unit when the received data unit does not
have the designated length of the data unit or when the received data unit
does not include a transceiver address which matches the address of the
selective call transceiver.
The forward radio channel has a plurality of forward channel frame
boundaries and a reverse channel frame boundary, which is relative to one
of the plurality of forward channel frame boundaries. The reverse channel
frame boundary is included in the command. The scheduled response time is
relative to the reverse channel frame boundary.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an electrical block diagram of a radio communication system, in
accordance with the preferred embodiment of the present invention.
FIG. 2 is an electrical block diagram of a fixed receiver, in accordance
with the preferred and first alternative embodiments of the present
invention.
FIG. 3 is an electrical block diagram of a fixed system receiver 107, in
accordance with second and third alternative embodiments of the present
invention.
FIG. 4 is a timing diagram of forward and reverse channel radio signals for
a first type of the radio communication system, in accordance with the
preferred embodiment of the present invention.
FIG. 5 is a timing diagram of forward and reverse channel radio signals for
a second type of the radio communication system, in accordance with the
preferred embodiment of the present invention.
FIG. 6 is a timing diagram of forward and reverse channel radio signals for
a third type of the radio communication system, in accordance with the
second alternative embodiment of the present invention.
FIG. 7 is a flow chart for generating the control signal which enables
reception of the reverse channel radio signal, in accordance with the
preferred embodiment of the present invention.
FIG. 8 is a flow chart for testing and routing received data units, in
accordance with the preferred embodiment of the present invention.
FIG. 9 is an electrical block diagram of a fixed system receiver in
accordance with a fourth alternative embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1, an electrical block diagram of a radio communication
system 100 is shown in accordance with the preferred embodiment of the
present invention. The radio communication system 100 comprises a message
input device, such as a conventional telephone 101, connected by a
conventional public switched telephone network (PSTN) 108 to a system
controller 102. The system controller 102 oversees the operation of at
least one radio frequency transmitter/receiver 103 and at least one fixed
system receiver 107, and encodes and decodes inbound and outbound
telephone addresses into formats that are compatible with land line
message switch computers and personal radio telephone addressing
requirements, such as cellular message protocols. The system controller
102 also functions to encode paging messages for transmission by the radio
frequency transmitter/receiver 103. Telephony signals and data messages
are transmitted from and received by a conventional antenna 104 coupled to
the radio frequency transmitter/receiver 103, and are received by a
conventional antenna 109 coupled to the fixed system receiver 107, which
by a unique design recovers the data messages with improved throughput and
reduced falsing. The telephony signals are transmitted to and received
from a conventional personal radio telephone 105. The radio frequency
transmitter/receiver 103 is also used to transmit data paging messages to
a portable receiving device 106. Acknowledgments and data messages are
transmitted by the radio telephone 105 and the portable receiving device
106, received by the antennas 104 and 109, and coupled to the system
controller 102.
It should be noted that the system controller 102 is capable of operating
in a distributed transmission control environment that allows mixing
conventional cellular, simulcast, master/slave, or other coverage schemes
involving a plurality of radio frequency transmitter/receivers 103,
conventional antennas 104, fixed system receivers 107, and conventional
antennas 109, for providing reliable radio signals within a geographic
area as large as a nationwide network. Moreover, as one of ordinary skill
in the art would recognize, the telephonic and selective call radio
communication system functions may reside in separate system controllers
102 which operate either independently or in a networked fashion.
It should also be noted that the radio frequency transmitter/receiver 103
may comprise the fixed system receiver 107 coupled to a conventional radio
frequency transmitter.
It will be appreciated that other selective call radio terminal devices
(not shown in FIG. 1), such as conventional mobile cellular telephones,
mobile radio data terminals, mobile cellular telephones having attached
data terminals, or mobile radios (trunked and non-trunked) having data
terminals attached, are also able to be used in the radio communication
system 100. In the following description, the term "selective call
transceiver" will be used to refer to the personal radio telephone 105, or
the portable transmitting/receiving device 106, a mobile cellular
telephone, a mobile radio data terminal, a mobile cellular telephone
having an attached data terminal, or a mobile radio (conventional or
trunked) having a data terminal attached. Each of the selective call
transceivers assigned for use in the radio communication system 100 has an
address assigned thereto which is a unique selective call address. The
address enables the transmission of a message from the system controller
102 only to the addressed selective call transceiver, and identifies
messages and responses received at the system controller 102 from the
selective call transceiver. Furthermore, each of one or more of the
selective call transceivers also has a unique telephone number assigned
thereto, the telephone number being unique within the PSTN 108. A list of
the assigned selective call addresses and correlated telephone numbers for
the selective call transceivers is stored in the system controller 102 in
the form of a subscriber data base.
The system controller 102 queues data and stored voice messages for
transmission to the selective call transceivers, connects telephone calls
for transmission to the selective call transceivers, and receives
acknowledgments, data responses, data messages, and telephone calls from
the selective call transceivers. The subscriber data base in the system
controller 102 stores information relevant to each subscriber's selective
call transceiver, including a correlation between the unique address
assigned to each selective call transceiver and the telephone number used
within the PSTN 108 to route messages and telephone calls to each
selective call transceiver, as well as other subscriber determined
preferences, such as hours during which messages are to be held back from
delivery to the selective call transceiver.
The system controller 102 schedules transmissions of messages and
acknowledgments from the selective call transceivers. These transmissions
include demand type transmissions from the selective call transceivers,
such as acknowledgments to messages which have been transmitted by the
system controller 102 and responses to messages such as status inquiries
transmitted from the system controller 102. The scheduled transmissions
can also include non-demand transmissions from the selective call
transceivers, such as messages being held by the selective call
transceivers, about which the selective call transceivers have informed
the system controller 102 within a previous message or acknowledgment
transmitted to the system controller 102 by the selective call
transceiver. The use of reverse channel scheduling under certain
circumstances improves the throughput of the reverse channel in comparison
to that achievable for an unscheduled, random input reverse channel
organization scheme such as that used in an ALOHA system, well known to
one of ordinary skill in the art. As will be described in more detail
below, a scheduled reverse channel may be a portion of the total time
available in a half duplex single frequency radio channel (a single radio
carrier frequency which is time shared for both forward and reverse
channels). Alternatively, the scheduled reverse channel may be some
portion of the time available, or all of the time available, in a second
radio carrier frequency which is different than the forward channel radio
frequency. Methods for identifying scheduled times will be described
below.
The system controller 102 is preferably a model E09PED0552 PageBridge.RTM.
paging terminal manufactured by Motorola, Inc., of Schaumburg Ill.,
modified with special firmware elements in accordance with the preferred
embodiments of the present invention, as described herein. The system
controller alternatively could be implemented using a MPS2000.RTM. paging
terminal manufactured by Motorola, Incorporated of Schaumburg, Ill. The
subscriber data base may alternatively be implemented as magnetic or
optical disk memory, which may alternatively be external to the system
controller 102.
Referring to FIG. 2, an electrical block diagram of the fixed receiver 107
is shown, in accordance with a preferred embodiment of the present
invention. The fixed receiver 107 comprises a combined receiver 205, which
is a radio frequency receiver operating at a first radio carrier frequency
for receiving forward and reverse radio channel signals, as will be
described more fully below, a response timer 215, a telephone interface
225, a routing controller 220, and the antenna 109. The antenna 109 is
coupled to a first input of the combined receiver 205. A first output 207
of the combined receiver 205 is coupled to the response timer 215 and a
second output 209 of the combined receiver 205 is coupled to the routing
controller 220. A control signal is generated by the response timer 215
and is coupled a second input 213 of the combined receiver 205. An output
211 of the combined receiver 205 is coupled to the routing controller 220.
The routing controller 220 has an output coupled to the telephone
interface 225. The telephone interface 225 has an output which is coupled
to the system controller 102, through a private network or the PSTN 108.
The fixed system receiver 107 includes unique functions which disable
reception to reduce falsing and which test responses received from the
selective call transceivers to improve throughput, as will be more fully
described below.
Referring again to FIG. 2, in a first alternative embodiment of the present
invention, the routing controller 220 is omitted and the output 211 of the
combined receiver 205 is coupled directly to the telephone interface 225.
The second output 209 of the combined receiver 205 is not used.
The fixed system receiver 107 in accordance with the preferred and first
alternative embodiments of the present invention preferably comprises a
Nucleus.RTM. model receiver manufactured by Motorola, Inc. of Schaumburg,
Ill., with unique functions added to the standard model. The unique
functions are provided by firmware routines developed in accordance with
techniques well known to one of ordinary skill in the art.
The fixed system receiver 107, in accordance with the preferred and first
alternative embodiment of the present invention, operates in a first type
or a second type of radio communication system 100. In the first type of
radio communication system 100, a first radio carrier frequency is time
shared by a forward channel, which is for transmitting information from
the transmitter/receivers 103 in a forward channel radio signal to one or
more identified selective call transceivers, and a reverse channel, which
is for transmitting scheduled responses from the identified selective call
transceivers in reverse channel radio signals to the transmitter/receivers
103. The antenna 109 intercepts the forward channel radio signal, which
includes telephony signals, digital messages, and commands. The combined
receiver 205 receives, demodulates and decodes the commands included in
the forward channel radio signal. From information included in the
commands, the response timer 215 generates the control signal, which
enables and disables the combined receiver 205 during the reverse channel
time of the first radio frequency. When the combined receiver 205 is
enabled by the control signal, the combined receiver 205 receives and
demodulates radio signals which contain scheduled responses transmitted by
the selective call transceivers.
In the preferred embodiment of the present invention, the scheduled
responses are coupled to the routing controller 220, wherein tests are
performed on the scheduled responses. When tests results are successful,
the scheduled responses are coupled to the telephone interface 225,
wherein the scheduled responses are used to modulate signals, such as
modem signals, which are transmitted to the system controller 102. When
the tests are not successful, the scheduled responses are processed no
further. In the first alternative embodiment of the present invention, the
scheduled responses are not tested, and are coupled directly to the
telephone interface 225. The scheduled responses include responses from
the selective call transceivers such as message and/or acknowledgment
information.
In the second type of radio communication system 100, the forward radio
channel and reverse radio channel are at two different radio frequencies,
and at least one of the transmitter/receivers 103 transmits the commands
in two radio signals: a forward channel radio signal having a first radio
carrier frequency which is a forward channel radio frequency and a reverse
channel radio signal having a second radio carrier frequency which is a
reverse channel radio frequency, although the forward and reverse
transmissions of the commands are not necessarily simultaneous. Thus, in
the radio communication system 100 of the first and second types, only one
frequency need be received to recover the commands and the scheduled
responses, which are used to generate the control signal and perform the
tests of the responses, because the commands are transmitted at the same
frequency as the scheduled responses.
Referring to FIG. 3, a block diagram of the fixed system receiver 107 is
shown in accordance with a second alternative embodiment of the present
invention. The fixed system receiver 107 shown in FIG. 3 differs from the
fixed system receiver 107 shown in FIG. 2 in that a separate forward
receiver 305 and reverse receiver 310 perform the functions performed by
the combined receiver 205 of the preferred embodiment of the present
invention. A first output 207 of the forward receiver 305 is coupled to
the response timer 215 and a second output 209 of the forward receiver 305
is coupled to the routing controller 220. A control signal is generated by
the response timer 215 and is coupled to a second input 213 of the reverse
receiver 310. An output 311 of the reverse receiver 310 is coupled to the
routing controller 220. The routing controller 220 has an output coupled
to the telephone interface 225. The telephone interface 225 has an output
which is coupled to the system controller 102, through the private network
or the PSTN 108.
Referring again to FIG. 3, in the fixed system receiver 107 in accordance
with a third alternative embodiment of the present invention, the routing
controller 220 is omitted and the output 311 of the reverse receiver 310
is coupled directly to the telephone interface 225. The second output of
the forward receiver 305 is not used.
The fixed system receiver 107 in accordance with the second and third
alternative embodiments of the present invention preferably comprises two
Nucleus.RTM. model receivers manufactured by Motorola, Inc. of Schaumburg,
Ill., with unique functions added to the standard model. The unique
functions are provided by firmware routines developed in accordance with
techniques well known to one of ordinary skill in the art.
The fixed system receiver 107, in accordance with the second alternative
embodiment of the present invention, operates in a third type of radio
communication system 100. In the third type of radio communication system
100, a forward channel radio frequency is used for transmitting
information from the transmitter/receivers 103 in a forward channel radio
signal to one or more identified selective call transceivers, and a
reverse channel radio frequency, which is different than the forward
channel radio frequency, is used for transmitting responses from the
identified selective call receivers in a reverse channel radio signal to
the transmitter/receivers 103. The antenna 109 intercepts the forward
channel radio signal, which includes telephony signals, digital messages,
and commands. The forward receiver 305 receives, demodulates and decodes
the commands included in the forward channel radio signal. From
information included in the commands, the response timer 215 generates the
control signal, which enables and disables the reverse receiver 310. When
the reverse receiver 310 is enabled by the control signal, the reverse
receiver 310 receives and demodulates radio signals which contain
scheduled responses transmitted by the identified selective call
transceivers.
The scheduled responses are processed in the second and third alternative
embodiments of the present invention, in an identical manner in which
scheduled responses are processed, respectively, in the preferred
embodiment and first alternative embodiment of the present invention,
which are described more fully below.
Referring to FIG. 4, a timing diagram 400 shows forward and reverse channel
radio signals for the first type of radio communication system, in
accordance with the preferred embodiment of the present invention. The
forward channel radio signal, which is transmitted during a forward
channel frame 420, and the reverse channel radio signals, which are
transmitted during a reverse channel frame 430, are at a first radio
carrier frequency.
The forward channel frame 420 duration is from a forward channel frame
boundary 401 to a reverse channel frame boundary 402 during which
transmissions of a forward channel radio signal are made from the
transmitter/receiver 103 to one or more of the identified selective call
transceivers in the first type of radio communication system 100. The
forward channel radio signal comprises one or more sequential radio
signals transmitted from the transmitter/receiver 103. A forward channel
frame synchronization word 403 and a plurality of forward channel messages
404, 405 are transmitted within the forward channel radio signal by the
transmitter/receiver 103. The reverse channel frame 430 duration is from
the reverse channel frame boundary 402 to the next forward channel frame
boundary 401 and includes a plurality of the slot times. A plurality of
scheduled responses 406, 410, 412, 413, 414 are transmitted as data units,
each data unit extending over one or more slot times. For example,
scheduled response 410 is four slot times, scheduled response 412 is five
slot times, and scheduled response 413 is two slot times. Each of the
plurality of scheduled responses 406, 410, 412, 413, 414 is a radio signal
transmitted from one of the identified selective call transceivers in
response to a command 455 which is completed in one of the forward channel
messages 404, 405. Scheduled response 410 is transmitted by one of the
selective call transceivers simultaneously with portions of scheduled
responses 412 and 413, which are transmitted by other selective call
transceivers. Scheduled response 410 is an example of a scheduled response
which overlaps, in time, other scheduled responses 412, 413. A scheduled
response overlap condition will occur, for example, when the system
controller 102 schedules different selective call transceivers to transmit
scheduled responses, of which at least some parts are expected to be
received at the same time by different geographically separated base
receivers. From information received in the command 455, the response
timer 215 in the fixed system receiver 107 generates response periods 408,
411, which are described more fully below.
Each frame synchronization word 403 contains a frame sync pattern that
marks the forward channel frame boundary 401 as well as information
describing the time offset to the reverse channel frame boundary 402, as a
number of slot times. The start time of each forward channel message 404
is defined relative to the forward channel frame boundary 401, for
example, by a number of slot times. A command 455 is included in one or
more of the forward channel messages 404, identifying one of the selective
call transceivers by a selective call address of the identified selective
call transceiver, as well as a scheduled response time at which the
identified selective call transceiver transmits a scheduled response in a
reverse channel radio signal, the scheduled response comprising a data
unit. The command 455 includes a designated length of the data unit. The
forward channel messages 404 also may include data 457, such as a
alphanumeric information message. The start time of each scheduled
response 406, 410, 412, 413, 414 is defined relative to the reverse
channel frame boundary 402.
Synchronization and timing information required by the selective call
transceivers in the radio communication system 100 for both receiving on
the forward channel frame and transmitting on the reverse channel frame is
determined from the forward channel frame synchronization word 403 and the
forward channel messages 404. When a selective call transceiver receives
the forward channel radio signal, the selective call transceiver processes
the forward channel message 404 included in the forward channel radio
signal when the forward channel message 404 includes the selective call
address of the selective call transceiver, thus identifying the selective
call transceiver for processing the forward channel message 404. When a
command 455 is received within the forward channel message 404, or in a
plurality of forward channel messages, processed by the identified
selective call transceiver, the identified selective call transceiver then
transmits one of the scheduled responses 406, 410, 412, 413, 414 with the
designated data unit length and at the scheduled response time commanded
by the system controller 102 in the command 455. Correspondence between
the commands 455 received by identified selective call transceivers in the
forward channel messages 404 and the scheduled responses 406, 410, 412,
413, 414 from the identified selective call transceivers is indicated in
FIG. 4 by arrowed lines from forward channel messages 404, 405 to the
scheduled responses 406, 410, 412, 413, 414, of which an example is line
415, which connects from a command 455 completed in forward message 405 to
scheduled response 414. Another example is line 416, which connects from a
command 455, not shown in FIG. 4, that is completed in an earlier forward
channel frame than the forward channel frame 420 shown in FIG. 4, to one
of the scheduled response 406 in FIG. 4. Another example is line 417 which
indicates connection from a command 455, not shown in FIG. 4, that is
completed in an earlier forward channel frame than the forward channel
frame 420 shown in FIG. 4, to a scheduled response that is in a later
reverse channel frame than those shown in FIG. 4.
Each scheduled response 406, 410, 412, 413, 414 transmitted from an
identified selective call transceiver is completely self contained in that
it includes all of the information required by the fixed system receiver
107 to detect and decode the scheduled response 406, 410, 412, 413, 414.
That is, the scheduled response 406, 410, 412, 413, 414 each include a
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